Immunological analysis methods are widely used in clinical tests of serum, plasma, urine and the like since they are capable of more simply and quickly performing measurements by using an automatic analyzer.
In order to expand the use of immunological analysis methods, a reagent which has higher detection sensitivity in a low-value range and reliability than existing reagents may be demanded. Means for adding a surfactant to an immunological analysis reagent are known; however, they are often used as a means for controlling the reactivity to avoid matrix effects and the like or as a means for amplifying the change in absorbance (see Patent Documents 1 and 2).
As a method of expanding the measurable range of an immunological analysis reagent, there are a method of raising the detection upper limit of the measurement range and a method of lowering the detection lower limit.
For increasing the sensitivity by lowering the detection lower limit in the measurable range of an immunological analysis reagent, there is a method by which the sensitivity in a low-value range is increased by increasing the amount of immunobilized on particles, antibodies or antigens that are contained in the reagent. However, even when the sensitivity in a low-value range is increased, if the reproducibility is poor, good measurement accuracy in a low value-range would not be attained.
When a highly reactive component is used to increase the sensitivity in a low-value range, there are cases where the reagent stability is deteriorated and agglutination reaction proceeds during storage of the reagent due to autoagglutination, or agglutination reaction may proceed also in the blank sample due to the occurrence of non-specific agglutination.
When the sensitivity in a low-value range is increased, for example, in an automatic analyzer used for measuring the change in absorbance, since there is set an upper limit in the change in absorbance, the sensitivity in a high-value range may be limited, so that a broad measurement range may not be attained.
Since the above-described problems arise when trying to lower the detection lower limit of a measurement range, it is difficult to expand a measurable range.